1. The Field of the Invention
The present invention relates generally to directly modulated lasers. More particularly, embodiments of the invention relate to methods and systems for compensating slow chirp in the frequency chirp modulation response of directly modulated lasers.
2. The Relevant Technology
Fiber optic communication systems use a variety of transmitters to convert electrical digital bits of information into optical signals that are sent through optical fibers. On the other end of the optical fiber is a receiver that converts the optical signal to an electrical signal. The transmitters modulate the signals to form bits of 1s and 0s so that information or data may be carried through the optical fiber. There are a variety of transmitters that modulate the signal in different ways. For example, there are directly modulated transmitters and indirectly modulated transmitters. Directly modulated transmitters offer a compact system having large response to modulation and are integratable. Directly modulated transmitters are also generally less expensive than externally modulated transmitters, which require an intensity modulator, usually LiNbO3, following the laser.
One of the drawbacks of a directly modulated transmitter is that its output is highly chirped. Chirp is the rapid change in optical frequency or phase that accompanies an intensity modulated signal. Chirped pulses become distorted after propagation through tens of kilometers of dispersive optical fiber, increasing system power penalties to unacceptable levels. There are various types of chirp exhibited by directly modulated transmitters, including transient chirp, adiabatic chirp, and slow chirp. Slow chirp generates a low frequency roll-off in the frequency modulation response of directly modulated transmitters and slows rise and fall time of emitted optical signals in the time domain. Slow chirp is generally attributed to intrinsic physical properties of the transmitter, such as carrier transport and spatial hole burning.
The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced